1. Field of the Invention
The invention relates to the field of apparatus and method for using light emitting diodes (LED) or other light sources of differing wavelengths in an approximately unitized beam, sharing similar angle space.
2. Description of the Prior Art
Color projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. More recently, presentations using multimedia projection systems have become popular for conducting sales demonstrations, business meetings, and classroom instruction. In a common operating mode, multimedia projection systems receive analog video signals from a personal computer (“PC”). The video signals may represent still, partial-, or full-motion display images of a type rendered by the PC. The analog video signals are typically converted in the projection system into digital video signals, and the signals are electronically conditioned and processed to control an image-forming device, such as a liquid crystal display (“LCD”) or a digital micromirror device (“DMD”).
A popular type of multimedia projection system employs a broad spectrum light source and optical path components upstream and downstream of the image-forming device to project the image onto a display screen.
However, the optical performance of conventional projectors is often less than satisfactory. For example, suitable projected image brightness is difficult to achieve, especially when using compact portable color projectors in a well-lighted room. The projectors typically use high intensity arc lamps as their light source and then filter out all of the light except for blue, green, and red light and employ three separate light paths or some forms of sequential color modulator to coordinate color image data. Such white light systems typically use a series of dichroic mirrors to fraction the light into red, green and blue wavelengths and then remix the light from each beam after passing each through an LCD mask which as been configured to provide a red, green and blue component of the final desired image. The optical path lengths are long and there are a number of reflections and filtration steps which must be performed with resulting loss in intensity and resolution. The physical package which must be provided for such a system can be large.
Because LCD displays have significant light attenuation and triple path color light paths are heavy and bulky, portable multimedia projectors typically employ DMD displays in a single light path configuration. Producing a projected color image with this configuration typically requires projecting a frame sequential image through a sequential color modulator, such as a color wheel.
Another form of color illuminator combines red, green, blue, cyan and amber colored LED sources in order to increase brightness in a complex reflected optical path to mix the resultant light in an integrator rod. Again the optical path ways are long, the optical system is necessarily physically large and the overall performance is still subject to intensity and collimation losses. In this case the output of the integrator rod is a single color and a plurality of such color illuminators must be employed to obtain a large scale pixel image.
What is needed is a some kind of a controllable color light source which is not subject to the inherent disadvantages of such prior art displays or other conventional colored light systems.